1. Field of the Invention
The present invention relates to a fuel injection control device for a common-rail diesel engine or the like.
2. Description of the Related Art
In common-rail diesel engines, two-stage injection comprising pilot injection and main injection is performed, particularly to prevent white smoke and noise from being emitted between start-up and warm-up.
In conventional practice, the pilot injection quantity is determined in accordance with the PQ map like that shown in FIG. 7 of the accompanying drawings. In this map, water temperature TW (xc2x0 C.) is plotted on the horizontal axis, and pilot injection quantity PQ is plotted on the vertical axis. The diagram on the map constantly varies with the operating state of the engine, as will be described below. Solid line (a) designates a given moment in time, but broken line (b) is also possible, depending on the operating state of the engine.
The area inside the map is divided into three regions by two set water temperatures LTW and HTW (LTW less than HTW). The regions corresponding to TWxe2x89xa6LTW, TWxe2x89xa7HTW, and LTW less than TW less than HTW are referred to as a low-temperature area, high-temperature area, and intermediate area, respectively. In the low-temperature area, the pilot injection quantity PQ does not depend on water temperature and remains constant (LLPQ). Similarly, the pilot injection quantity PQ in the high-temperature area does not depend on water temperature and remains constant (HHPQ). It should be noted that LLPQ greater than HHPQ. The values inside the intermediate area are obtained by the two-point interpolation of LLPQ and HHPQ, and the diagram has a linear shape, as shown in the drawing.
The map is used to calculate the LLPQ and HHPQ values on the basis of the rotational engine speed NE and total injection quantity Q. This is indicated by the use of the smaller subscripts (NE, Q) in the drawing. Thus, LLPQ and HHPQ vary with the operating state of the engine, and the diagram on the map constantly varies as a result.
FIG. 8 of the accompanying drawings illustrates a flowchart for calculating the pilot injection quantity. The rotational engine speed NE, total injection quantity Q, and water temperature TW are first sensed or computed in step 401, and LLPQ and HHPQ are calculated in step 402. After being thus defined, the PQ map shown in FIG. 7 is used in the subsequent step 403 to calculate the pilot injection quantity PQ on the basis of the water temperature TW.
An engine commonly emits undesirable white smoke when operating at a low ambient temperature. Methods in which spark advance is employed for the fuel injection timing have been suggested to counter this phenomenon, but these methods increase the noise level. For this reason, pilot injection has become an extremely effective means for keeping white smoke and noise within prescribed limits at low ambient temperatures.
With these conventional techniques, however, the pilot injection quantity is determined without taking into account the ambient temperature in any way. Consequently, these techniques cannot yet be considered adequate for controlling pilot injection, and keeping white smoke and noise within prescribed limits is still a difficult task.
The present invention provides an engine fuel injection control device for performing prescribed pilot injection and main injection on the basis of the operating state of the engine, comprising pilot injection correction means for correcting the pilot injection quantity on the basis of the ambient temperature.
This arrangement allows the pilot injection quantity to be selected in accordance with the ambient temperature, and pilot injection to be controlled optimally and adequately.
The pilot injection correction means preferably takes corrective action to increase the pilot injection quantity if the ambient temperature falls below a specified level.
The pilot injection correction means preferably operates such that no corrective action is taken if the water temperature is greater a first specified value on a high-temperature side.
The pilot injection correction means preferably operates such that no corrective action is taken if the water temperature is less than a second specified value on a low-temperature side.